Targeted gene expression as a means of altering cell fates and generating dominant phenotypes

TLDR

The authors designed a system for targeted gene expression that enables selective activation of any cloned gene in diverse tissue‑ and cell‑specific patterns. The system uses random insertion of GAL4 into the Drosophila genome to drive expression from diverse enhancers, then activates genes containing GAL4 binding sites in those cells, allowing directed misexpression and generation of dominant phenotypes in adults. Using the GAL4 system, the authors expanded embryonic expression of even‑skipped, showing it represses wingless and converts cuticle‑secreting cells into denticle‑secreting cells, and demonstrated that activated Dras2 expression produces dominant eye and wing defects useful for genetic screens.

Abstract

ABSTRACT We have designed a system for targeted gene expression that allows the selective activation of any cloned gene in a wide variety of tissueand cell-specific patterns. The gene encoding the yeast transcriptional activator GAL4 is inserted randomly into the Drosophila genome to drive GAL4 expression from one of a diverse array of genomic enhancers. It is then possible to introduce a gene containing GAL4 binding sites within its promoter, to activate it in those cells where GAL4 is expressed, and to observe the effect of this directed misexpression on development. We have used GAL4-directed transcription to expand the domain of embryonic expression of the homeobox protein even-skipped. We show that even-skipped represses wingless and transforms cells that would normally secrete naked cuticle into denticle secreting cells. The GAL4 system can thus be used to study regulatory interactions during embryonic development. In adults, targeted expression can be used to generate dominant phenotypes for use in genetic screens. We have directed expression of an activated form of the Dras2 protein, resulting in dominant eye and wing defects that can be used in screens to identify other members of the Dras2 signal transduction pathway.